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Timothy W. Coolong and William M. Randle

(CalBiochem, EMD Biosciences, San Diego, CA). The remaining pellet was suspended in 40 mL of 0.05 m sodium oxalate, 0.05 m ammonium oxalate, and 0.05 m sodium acetate, pH 5.2, and incubated for 90 min at 60 °C to obtain chelator-soluble pectin (CSP). The

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Jeff S. Kuehny, Patricia C. Branch, and Felix J. Landry

Nitrate nitrogen has been recommended as the best form of nitrogen for the production of poinsettia while ammonium and urea have been reported to be deleterious to poinsettia growth. Recent studies have indicated that lower nitrogen and leaching levels will produce quality poinsettias. Poinsettias were grown with 21–7–7 Acid Special (9.15% NH4, 11.85% urea), 20–10–20 Peat-lite Special (7.77% NH4, 12.23% NO3), 15-220 plus Ca and Mg (1.5% NH4, 12.7% NO3, 0.8% urea), and 15–5–15 Excel CalMag (1.2% NH4, 11.75% NO3, 2.05% urea) applied at 200 mg·L-1. Plants were fertigated by drip irrigation with zero leachate. There were no significant differences between fertilizer treatments for plant height, width, bloom diameter, and dry weight. Electrical conductivity and pH did vary significantly between treatments; however, this did not effect plant growth. Thus, by using lower nitrogen levels and zero leachate, quality poinsettias can be grown with commercial fertilizers high in ammonium/urea or high in nitrate nitrogen, or ammonium and nitrate in combination.

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Charles J. Graham and Gregory L. Reighard

A field experiment was conducted to assess the effects of several foliar nutrient sprays on the vegetative growth of 'Jefferson' peach budded on 'Nemaguard' and 'Lovell' rootstocks planted on a site with a history of Peach Tree Short Life. The trees received foliar applications of 2 mN solutions of ammonium citrate, calcium citrate, calcium lactate, calcium phosphate, or a water control at 3 week intervals from April to August. Vegetative growth measurements were taken after one growing season. Trunk cross-sectional area (TCSA) was significantly increased by ammonium citrate (TCSA=20.35 cm2), calcium citrate (TCSA=20.03 cm2), and calcium lactate (TCSA=19.91 cm2) when compared to controls (TCSA=16.75 cm2). Trees on 'Nemaguard' responded more to treatments than those on 'Lovell'. All nutrient sprays increased TCSA, lateral growth, terminal growth, and total tree growth on 'Nemaguard' rootstock. Terminal growth increased 12-36%, and total tree growth increased 18-51 % compared to control trees, but only ammonium citrate applications were significantly greater. Lateral growth and TCSA of treated trees increased 65-168% and 17-28%, respectively.

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Xiaojie Zhao, Guihong Bi, Richard L. Harkess, and Eugene K. Blythe

Nitrogen is an important macronutrient needed by plants and often required in the highest amount of all the mineral elements. Normally, N is supplied to plants in form of nitrate (NO 3 − ), ammonium (NH 4 + ), or urea [CO(NH 2 ) 2 ]. Both the rate

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Silvia Jiménez Becker, Maria Teresa Lao, and Mari Luz Segura

+ and N-NO 3 – are important nitrogen sources for plant growth ( Marschner, 1995 ). Most plants can use either, or both, ammonium and nitrate, and the effects of the applied N form depend on the ontogenic development of the plant, the plant species

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Allen V. Barker and Kathleen M. Ready

Studies of ethylene evolution by tomato (Lycopersicon esculentum Mill.) fruit were conducted with plants receiving NH4-N or NO3-N nutrition. Fruit of plants grown with NH4-N had a higher occurrence of blossom-end rot (BER), higher NH4-N concentrations, and higher ethylene evolution rates than fruit from plants grown with NO3-N. Fruit of plants grown with NO3-N showed no enhancement in ethylene evolution with BER development. Fertilizing these plants with Ca(NO3)2 doubled the average Ca concentration of fruit and restricted BER development. Ammonium suppressed Ca accumulation in fruit relative to those grown with NO3-N. Ethylene evolution increased as fruit from plants receiving NO3-N ripened, but without a concomitant increase in NH4-N concentrations in the fruit. Ammonium accumulation in fruit induced BER and enhanced ethylene evolution. These relationships were unique, for NH4-N accumulation did not seem to be a naturally occurring phenomenon in ripening fruit or in fruit that have BER arising from other causal factors.

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Yin-Tung Wang and Yao-Chien Alex Chang

15K–2.2P–12.5K (N = 78% nitrate + 8% ammonium + 14% urea), as N concentration increased from 0 to 200 mg·L −1 , leaf span, leaf number, total leaf length, and flower count all increased ( Wang, 2010 ) ( Fig. 1 ). In this study, the increase in flower

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Wenqi You and Allen V. Barker

The herbicidal action of foliar applications of glufosinate-ammonium (GLA) is due to toxic accumulation of unassimilated NH4 + in leaves; however, the effects of root-applied GLA on NH4 + accumulation and plant growth are unknown. In a dose-response hydroponics experiment, tomato (Lycopersicon esculentum Mill.) plants were grown in nitrate-based solutions with GLA added at 0, 6, 12, 25, or 50 mg·L-1. To observe plant responses to an exogenous NH4 + source with herbicide-induced responses, plants were grown in an NH4 +-based solution without GLA addition. At 6 days after treatment (DAT), GLA in solution at 25 mg·L-1 produced partial leaf wilting, chlorosis, and necrosis of foliage, and at 50 mg·L-1, plants were fully wilted and necrotic. Ammonium (NH4 +-N) concentration in shoots at 6 DAT increased from 0 to 6 mg·g-1 fresh weight with increasing GLA in the nutrient solution. Ethylene evolution doubled (from 4 to 8 nL·g-1·h-1, fresh weight) with increases in GLA from 0 to 25 mg·L-1 but declined with apparent plant death with GLA at 50 mg·L-1. Other treatments, including NH4 + nutrition, did not induce toxicity symptoms in leaves or give increases in NH4 + accumulation or ethylene evolution during the 6 days of the experiment. In a time-course experiment, tomato plants treated with GLA at 25 mg·L-1 were chlorotic at 4 DAT. Ethylene evolution (fresh weight basis) rose from an initial rate of 2.6 nL·g-1·h-1 to 8.3 nL·g-1·h-1 after 4 days. At 9 DAT, all plants receiving this treatment died. In the time-course experiment, an exogenous NH4 + treatment caused a slight inhibition in shoot fresh weight relative to NO3 - nutrition with no GLA but caused no visible symptoms and only slight enhancements in NH4 + accumulation and ethylene evolution over the 9-day period. Following GLA treatment, NH4 + accumulated in the shoots and increased sharply with time, whereas exogenous NH4 + led to NH4 + accumulation primarily in roots. Results suggest that GLA was absorbed by roots and translocated to shoots, where it initiated accumulation of NH4 + and ethylene evolution as indications of herbicidal action. Chemical name used: glufosinate-ammonium, GLA.

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Joseph J. King, Lloyd A. Peterson, and Dennis P. Stimart

Ammonium and NO3 uptake from hydroponic solutions containing 1 mm each of (NH4)2SO4 and Ca(NO3)2 were measured during development of Dendranthema ×grandiflorum (Ramat.) Kitamura `Iridon', `Sequoia', and `Sequest'. Nitrogen depletion from solutions approximated a 1 NH4: 1 NO3 ratio throughout a 90-day growth cycle (r = 0.96). Although harvest date cultivar interactions were significant for both forms of N, overall patterns of N uptake were similar among cultivars. Nitrogen removal from hydroponic solutions (milligrams per plant) was greatest from days 40 to 60; however, N removal (milligrams per gram of tissue dry weight) was greatest in the first month of development and decreased steadily until day 90. From day 40 to 60, new leaf development ceased while inflorescence buds developed to ≈1.0 cm in diameter. After this time, N uptake decreased rapidly as inflorescences expanded. Correlations between morphological changes and N demand could maximize the efficiency of applied N by matching form and application timing with plant needs.

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Anwar G. Ali and Carol J. Lovatt

The effects of different methods of sample preparation, extraction, and storage on the recovery of the combined pool of ammonia plus ammonium (NH3 + NH4 +) from `Washington' navel orange leaves previously incubated in solutions of increasing NH4 Cl concentrations were assessed. Procedures and instruments for quantifying NH3 + NH4 + were tested for their sensitivity, reproducibility, and freedom from interference by amino acids. Reliable recoveries of NH3 + NH4 + free from amino acid interference, were obtained with oven-dried (60C) leaves ground to pass through a 40-mesh screen, extracted by homogenization in 10% TCA or by shaking in 2% acetic acid, and then filtered and analyzed on the basis of differences in electrical conductance between the sample and the reference cell. Methods measuring NH3 + NH4 + in KCl extracts by reaction with salicylate-nitroprusside in the presence of hypochlorite were compromised by significant color formation due to amino acids. Using fresh or freeze-dried leaf samples resulted in lower recoveries than use of oven-dried samples. Storage at -20C of fresh or oven-dried leaf samples in 10% TCA before or after homogenization and filtration did not alter NH3 + NH4 + levels, whereas storage of these samples at 4C increased NH3 + NH4 + levels.